Aspartyl protease inhibitors are considered the most effective current drug in the fight against HIV infection. These inhibitors, however, require certain physicochemical properties in order to achieve good potency against the enzyme. One of these properties is high hydrophobicity. Unfortunately, this property results in poor aqueous solubility and low oral bioavailability.
U.S. Pat. No. 5,585,397 describes a class of sulfonamide compounds that are inhibitors of the aspartyl protease enzyme. These compounds illustrate the drawbacks concomitant to pharmaceutical compositions comprising hydrophobic aspartyl protease inhibitors. For example, VX-478 (4-amino-N-((2-syn,3S)-2-hydroxy-4-phenyl-2((S)-tetrahydrofuran-3-yl-oxycarbonylamino)-butyl-N-isobutyl-benzenesulfonamide) is an aspartyl protease inhibitor disclosed in the '397 patent. It has a relatively low aqueous solubility. While the oral bioavailability of this inhibitor in a “solution” formulation is excellent, the dosage of VX-478 in this form is severely limited by the amount of liquid present in the particular liquid dosage from, e.g., encapsulated into a soft gelatin capsule. A higher aqueous solubility would increase drug load per unit dosage of VX-478.
Currently, the solution formulation of VX-478 produces an upper limit of 150 mg of VX-478 in each capsule. Given a therapeutic dose of 2400 mg/day of VX-478, this formulation would require a patient to consume 16 capsules per day. Such a high pill burden would likely result in poor patient compliance, thus producing sub-optimal therapeutic benefit of the drug. The high pill burden is also a deterrent to increasing the amount of the drug administered per day to a patient. Another drawback of the pill burden and the concomitant patient compliance problem is in the treatment of children infected with HIV.
Furthermore, these “solution” formulations, such as the mesylate formulation, are at a saturation solubility of VX-478. This creates the real potential of having the drug crystallize out of solution under various storage and/or shipping conditions. This, in turn, would likely result in a loss of some of the oral bioavailability achieved with VX-478.
One way of overcoming these problems is to develop a standard solid dosage form, such as a tablet or a capsule or a suspension form. Unfortunately, such solid dosage forms have much lower oral bioavailability of the drug.
Thus, there is a need to improve the drug load per unit dosage form for aspartyl protease inhibitors. Such an improved dosage form would reduce the pill burden and increase patient compliance. It would also provide for the possibility of increasing the amounts of the drug administered per day to a patient.